A hybrid vehicle's performance may be based on performance of an engine and performance of a driveline integrated starter/generator (DISG). The hybrid vehicle's maximum torque curve (e.g., the hybrid vehicle's driveline torque at a torque converter impeller below which driveline torque is maintained at all times the maximum is in effect) may be a summation of the engine's maximum torque curve (e.g., engine torque below which engine torque is maintained at all times the maximum is in effect) and the DISG's maximum torque curve (e.g., electric machine torque below which electric machine torque is maintained at all times the maximum is in effect). A driver may request up to the combined maximum torque of the DISG and the engine during driving conditions. The engine may provide a rather consistent maximum torque at a predetermined speed. The engine's maximum torque varies as a function of barometric pressure, engine speed, engine temperature, and fuel combusted. On the other hand, the motor's maximum torque may vary more significantly based on motor temperature, battery state of charge (SOC), and motor speed. Consequently, when an engine's maximum torque curve is added to a DISG's maximum torque curve, the resulting maximum torque curve for the vehicle driveline may exhibit significant changes in maximum driveline torque over operating conditions.
A driver may notice significant changes in driveline torque over a driving cycle with a heavy accelerator pedal tip-in as SOC is reduced and as DISG maximum torque is reduced. For example, the hybrid vehicle may begin a drive cycle being able to accelerate at a first rate, and the hybrid vehicle may end the drive cycle being able to accelerate at a second rate, the second rate slower than the first rate. The driver may find the reduction in acceleration to be objectionable. Therefore, it may be desirable to provide more consistent vehicle performance over a drive cycle.
The inventors herein have recognized the above-mentioned disadvantages and have developed a driveline method, comprising: adjusting a maximum driveline torque threshold in response to driveline speed and a battery discharge power limit; and limiting driveline torque in response to the maximum driveline torque threshold.
By adjusting a maximum driveline torque threshold in response to driveline speed and battery discharge power limit (e.g., a battery discharge power level which the battery discharge power is prevented from exceeding), the technical result of improving driveline performance consistency may be achieved. For example, battery charge may be conserved at higher driveline speeds where electric machine output torque may be reduced by not supplying torque from the electric machine to the driveline. At lower speeds, the conserved charge may be used to provide torque to the driveline. In this way, it may be possible to increase the number of vehicle launches where the electric machine assists an engine to launch the vehicle. Consequently, a driver may experience fewer situations when the electric machine is unavailable or operating in a reduced torque mode during vehicle launch conditions.
The present description may provide several advantages. Specifically, the approach may improve driveline performance consistency. Further, the approach may provide driveline responses tailored for specific driving modes. Additionally, the approach may be applied to hybrid vehicles that include gasoline, diesel, or gaseous fueled engines.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.